Use of computer aided design (CAD) and analysis tools is a standard practice for modern electronic circuit designers. Electronic designs may be described using many different methodologies. Hardware description languages, such as very high speed integrated circuit (VHSIC) hardware description language (VHDL), Verilog—a language which has been standardized by the Institute of Electrical and Electronic Engineers (IEEE) as IEEE 1364—or another hardware description language may be used by a designer to describe a circuit. Graphically based systems such as schematic entry systems, physical layout tools, or other types of graphical tools may be used in some cases to describe a circuit.
Once the basic functionality of a circuit has been entered, computer-based tools may transform the description into a description with a lower level of abstraction. For example, a hardware description language may describe the operation of an arithmetic logic unit (ALU) using logical and/or arithmetical operations without any particular implementation in the gates or transistors being described by the designer. The computer tools may transform the ALU description into a set of NAND gates connected in a particular fashion. Another computer tool may then take the description of the set of interconnected NAND gates and generate a physical design describing many different layers of an integrated circuit that may create various metal-oxide-semiconductor field-effect transistors (MOSFET, or simply FET) interconnected by conductive traces.
Computer tools may be used at one or more stages of the process to analyze the circuit. At a very high level, some tools may perform a functional analysis, while other tools may perform a bit-accurate simulation of a binary value for each node of the design over time. Other computer analysis tools may perform various low-level analyses, such as timing analysis, crosstalk analysis, power analysis, transmission-line analysis, or other physical analysis. In the large, complex circuits which are common today, it may be difficult to perform such low-level analysis; the very large number of elements and nodes in the circuit means that analysis may require looking at a large number of combinations. In some cases, certain assumptions may be made to simplify the analysis, but may result in less accurate analysis.